The invention relates to a method of operating a CCD imager with a semiconductor body comprising a matrix of photosensitive elements arranged in rows and columns, and a system of CCD channels which extend in the matrix in the column direction and at at least one of the ends merge into a read-out register which extends adjacent the matrix parallel to the rows of the matrix, the matrix being divided at least in the column direction into two at least substantially equal segments which are each provided with a separately controllable system of electrodes for storing and transporting charge packets in said CCD channels.
The invention also relates to a CCD imager with a semiconductor body comprising a matrix of photosensitive elements arranged in rows and columns, and a system of CCD channels which extend in the matrix in the column direction and at at least one of the ends merge into a read-out register which extends adjacent the matrix parallel to the rows of the matrix, the matrix being divided at least in the column direction into two at least substantially equal segments which are each provided with a separately controllable system of electrodes for storing and transporting charge packets in said CCD channels.
Such a CCD imager and a method of operating said imager are known, for example, from the article "Tektronics Four Quadrant Readout 1024.times.1024 CCD Imager: First Test Results" by Delamere et al., published in SPIE Vol. 1071, Optical Sensors and Electronic Photography (1989) pp. 197-202. A "Full Frame" imager is described therein where the number of image elements or pixels corresponds to the number of image elements of a complete image. The matrix is provided with a horizontal read-out register on either side of the CCD channels so as to be able to read out such a large imager sufficiently quickly. The matrix is subdivided into two halves which each belong to one of the read-out registers, while each matrix half can be read out through the associated horizontal register. Each horizontal register in its turn may again comprise two parts with mutually opposed charge transport directions, each corresponding again to an adjoining quadrant of the matrix. Such constructions have the advantage that two halves or four quadrants of the matrix can be read out simultaneously instead of consecutively. As a result, the read-out time can be limited, also in the case of a very large imager with a very large number of pixels, as is often the case in a "Full Frame" imager. Although the matrix is subdivided into four quadrants, each having a separate read-out register, in most versions of a "Full Frame" imager, the present invention is not limited thereto, but it may also be applied to "Full Frame" imagers having a read-out register at one side of the matrix only, as will become apparent below.
Imagers of the kind described above differ from better known CCD imagers, known inter alia as imagers of the FT-type (Frame Transfer) or of the interline type, which are designed for recording or displaying moving images, through the absence of a memory section. For such applications, the imager is provided with a recording section and a memory section. In these known types, an image is recorded in the recording section and converted into a pattern of charge packets during a certain integration period. This pattern of charge packets is quickly moved into the memory section after the integration period and read out therein packet by packet. Since the memory section is screened from radiation, the change of the charge packets owing to absorption of radiation during read-out, often referred to as "smear", is very small. During read-out, an image can be taken up in the recording section again and converted into electric charges. The presence of the memory section renders it possible inter alia to record such a high number of images per unit time and convert them into electric charges that the video signals of moving images can be displayed on a TV screen or LCD screen, for example, as real-time pictures.